Double throat pulsation dampener for a compressor

ABSTRACT

A method of attenuating fluid dynamic pulsations that propagate through a flow of fluid at a convective velocity of the fluid, the pulsations having an organized vortical structure includes directing the flow to a pulsation dampener inlet having a first area and transitioning the organized vortical structure to a small-scale turbulent structure by squeezing the vorticies by passing the flow of fluid through a passage having a second area that is smaller than the first area, then rapidly expanding the flow of fluid by passing it into a chamber having a third area measured at an inlet of the chamber that is substantially larger than the second area. The method also includes discharging the flow of fluid from the chamber. The flow of fluid includes substantially attenuated fluid dynamic pulsations and acoustic pulsations that travel through the flow of fluid at the speed of sound.

RELATED APPLICATION DATA

The present application is a continuation of U.S. patent applicationSer. No. 11/111,269 filed Apr. 21, 2005, and entitled “Double ThroatPulsation Dampener for a Compressor,” the entire contents of which arefully incorporated herein by reference.

BACKGROUND

The present invention relates to pulsation dampeners used on oil freescrew compressors to suppress the pressure pulsations generated by thecompressor airend. A pulsation dampener reduces the mechanicalvibrations in the downstream piping system caused by the pressurepulsations originating from the outlet of the compressor. If thesepulsations are left undamped, the pulsations can damage the pipingsystem, coolers, moisture separator, valves and ancillary equipment.Pulsation dampeners reduce noise heard from the compressor by reducingthe pressure pulsations inside the piping system.

The venturis 10 and 15 shown in FIGS. 1-2 and 3-4, respectively, arecurrently used to reduce pressure pulsations. A venturi is a high passacoustical device. A high pass device attenuates pressure pulsationshaving low frequencies while allowing high frequency pressure pulsationsto pass through the device. Oil free compressor applications require alow pass acoustical device. A low pass acoustical device attenuates thehigh frequencies and allows low frequencies to pass through the device.The venturi does offer some attenuation at the higher frequencies, butthe attenuation is not sufficient (i.e., does not cover broad ranges offrequencies) to reduce all of the pulsations. Insufficient attenuatingof the high frequency pressure pulsations by the venturi have resultedin high noise levels, damage to check valves, cooler failures andringing piping systems.

SUMMARY

Some embodiments of the present invention provide a pulsation dampenerfor receiving a fluid medium comprising pressure pulsations. Thepulsation dampener can include a body having an inlet end and an outletend. The inlet end can include an inlet having a first cross-sectionalarea, and the outlet end can include an outlet. The pulsation dampenercan further include a fluid path defined at least partially by the bodyand extending between the inlet and the outlet. The fluid path caninclude a first contracting chamber positioned adjacent the inlet andhaving a second cross-sectional area, a first expansion chamberpositioned adjacent the first contracting chamber and having a thirdcross-sectional area, and a second contracting chamber positionedadjacent the first expansion chamber and having a fourth cross-sectionalarea. The fluid path can be configured such that the secondcross-sectional area is less than the first cross-sectional area and thethird cross-sectional area, and the fourth cross-sectional area is lessthan the third cross-sectional area.

In some embodiments of the present invention, a pulsation dampener forreceiving a fluid medium comprising pressure pulsations is provided. Thepulsation dampener can include a body having an inner surface, an inlet,and an outlet. The pulsation dampener can further include a fluid pathdefined at least partially by the inner surface of the body. The fluidpath can include a first chamber in fluid communication with the inletand having a first cross-sectional area, a second chamber positionedadjacent the first chamber and having a second cross-sectional areadifferent from the first cross-sectional area, and a third chamber influid communication with the outlet and positioned adjacent the secondchamber opposite the first chamber. The third chamber can include athird cross-sectional area different from the second cross-sectionalarea. The fluid path can be configured such that the secondcross-sectional area is greater than the first cross-sectional area andthe third cross-sectional area.

Some embodiments of the present invention provide a pulsation dampenerfor receiving a fluid medium comprising pressure pulsations. Thepulsation dampener can include a body having an inner surface, an inletend, and an outlet end. The inlet end can include an inlet having afirst cross-sectional area, and the outlet end can include an outlet.The pulsation dampener can further include a fluid path defined at leastpartially by the inner surface of the body and extending between theinlet and the outlet. The fluid path can include a first contractingchamber positioned adjacent the inlet and having a secondcross-sectional area, a first expansion chamber positioned adjacent thefirst contracting chamber opposite the inlet and having a thirdcross-sectional area, a second contracting chamber positioned adjacentthe first expansion chamber opposite the first contracting chamber andhaving a fourth cross-sectional area, and a second expansion chamberpositioned adjacent the second contracting chamber opposite the firstexpansion chamber and having a fifth cross-sectional area. The fluidpath can be configured such that the second cross-sectional area is lessthan the first cross-sectional area and the third cross-sectional area,and the fourth cross-sectional area is less than the thirdcross-sectional area and the fifth cross-sectional area.

In one construction, the invention provides a method of attenuatingfluid dynamic pulsations that propagate through a flow of fluid at aconvective velocity of the fluid, the pulsations having an organizedvortical structure. The method includes directing the flow to apulsation dampener inlet having a first area and transitioning theorganized vortical structure to a small-scale turbulent structure bysqueezing the vorticies by passing the flow of fluid through a passagehaving a second area that is smaller than the first area, then rapidlyexpanding the flow of fluid by passing it into a chamber having a thirdarea measured at an inlet of the chamber that is substantially largerthan the second area. The method also includes discharging the flow offluid from the chamber. The flow of fluid includes substantiallyattenuated fluid dynamic pulsations and acoustic pulsations that travelthrough the flow of fluid at the speed of sound.

In another construction, the invention provides a method of attenuatingpulsations produced by the operation of a compressor. Operation of thecompressor produces fluid dynamic pulsations that propagate through aflow of fluid at a convective velocity of the fluid and acousticpulsations that propagate through the flow of fluid at the speed ofsound. The method includes converting the fluid dynamic pulsations toacoustic pulsations by first constricting the flow of fluid and thenrapidly expanding the flow of fluid and attenuating the acousticpulsations by passing the flow of fluid through a converging divergingnozzle.

In yet another construction, the invention provides a method ofattenuating pulsations in a flow of fluid produced by the operation of acompressor. The method includes directing the flow of fluid to apulsation dampener inlet having a maximum diameter that defines a firstcross sectional area, constricting the flow of fluid by passing itthrough a constricting flow path having a minimum diameter that definesa second cross sectional area that is smaller than the first crosssectional area, and suddenly expanding the flow of fluid by dischargingthe flow of fluid into a chamber having an inlet cross sectional areathat is substantially larger than the second cross sectional area. Theinlet cross sectional area being measured immediately adjacent theminimum diameter of the constricting flow path. The method also includesgradually constricting the flow of fluid by passing it through a chamberflow path in which the cross sectional area gradually reduces to aminimum third cross sectional area, gradually expanding the flow offluid by passing it through an expanding flow path in which the crosssectional area gradually increases to a maximum fourth cross sectionalarea, and discharging the flow of fluid from the pulsation dampener viaan opening having an outlet cross sectional area that is about equal tothe fourth cross sectional area.

Other features and aspects of the invention will become apparent byconsideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a prior art first stage venturi.

FIG. 2 is a cross-sectional view of the prior art first stage venturi ofFIG. 1.

FIG. 3 is an isometric view of a prior art second stage venturi.

FIG. 4 is a cross-sectional view of the prior art second stage venturiof FIG. 3.

FIG. 5 is an isometric view of a pulsation dampener that is a firstembodiment of the present invention.

FIG. 6 is a cross-sectional view of the pulsation dampener of FIG. 5.

FIG. 7 is a schematic illustration of the pulsation dampener of FIG. 5.

FIG. 8 is an isometric view of a pulsation dampener that is a secondembodiment of the present invention.

FIG. 9 is a cross-sectional view of the pulsation dampener of FIG. 8.

FIG. 10 is a graph of transmission loss and pressure drop versusfrequency for the first stage venturi of FIGS. 1 and 2.

FIG. 11 is a graph of transmission loss and pressure drop versusfrequency for the second stage venturi of FIGS. 3 and 4.

FIG. 12 is a graph of transmission loss versus frequency for thepulsation dampener of FIGS. 5-7.

FIG. 13 is a graph of transmission loss versus frequency for thepulsation dampener of FIGS. 8-9.

DETAILED DESCRIPTION

The present invention will be described with reference to theaccompanying drawing figures wherein like numbers represent likeelements throughout. Certain terminology, for example, “top”, “bottom”,“right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and“rearward”, is used in the following description for relativedescriptive clarity only and is not intended to be limiting.

Referring to FIGS. 5-7, a pulsation dampener 20 that is a firstembodiment of the present invention will be described. The pulsationdampener 20 includes a body 22 having an inlet end 24 and an outlet end26, and an inner surface 17. The inner surface 17 of the body 22 definesa fluid path 21 that extends between the inlet end 24 and the outlet end26. In some embodiments, as shown in FIGS. 5 and 6, the dampener body 22has an approximately 90-degree angle configuration such that the inletend 24 is substantially perpendicular to the outlet end 26, and thefluid flow through the fluid path 21 changes direction by about 90degrees. However, the body may have other configurations. For example,in some embodiments, the body 22 includes a 45-degree configuration, ora straight configuration. In a straight configuration, the inlet end 24is substantially parallel to the outlet end 26, and the fluid flowthrough the fluid path 21 does not change directions.

In some embodiments, such as the embodiment illustrated in FIGS. 5 and6, the body 22 includes a one or more ribs 19 positioned to enhancestructural integrity of the body 22 and pulsation dampener 20. Forexample, the ribs 19 can be positioned on the outside of the body 22adjacent narrow regions of the fluid path 21 (e.g., contractingchambers, as described below), as shown in FIG. 5, to enhance thestructural integrity of the body 22 in those narrow regions.

In some embodiments, the dampener body 22 is a cast structure and may beprovided with a port 33 in fluid communication with the fluid path 21,positioned to assist in clean out of the body 22, and particularly, inremoval of media used in the casting process. The port 33 can be pluggedafter manufacture.

In some embodiments of the present invention, the pulsation dampener 20is a first stage dampener and has a flange 23 at the inlet end 24 and aflange 32 at the outlet end 26 for connection to the intended pipingsystem.

The inlet end 24 has an inlet 25 having an inlet cross-sectional areaS_(I). A fluid medium containing pressure pulsations, for example,compressed air from an oil free compressor airend, is directed intofluid path 21 of the pulsation dampener 20 through the inlet 25. Thefluid medium is thereafter contracted as it travels through a firstcontracting chamber 27 having a cross-sectional area S₁(e.g., theminimum cross-sectional area within the first contracting chamber 27)that is less than the inlet cross-sectional area S_(I). From the firstcontracting chamber 27, the fluid medium travels into a first expansionchamber 28 having a cross-sectional area S₂(e.g., the maximumcross-sectional area within the first expansion chamber 28) that isgreater than the cross-sectional area S₁of the first contracting chamber27. The fluid medium is again contracted as it flows to a secondcontracting chamber 29 having a cross-sectional area S₃(e.g., theminimum cross-sectional area within the second contracting chamber 29)that is less than the cross-sectional area S₂ of the first expansionchamber 28. Thereafter, the fluid medium flows into a second expansionchamber 30 having a cross-sectional area S₄(e.g., the maximumcross-sectional area of the second expansion chamber 30) that is greaterthan the cross-sectional area S₃ of the second contracting chamber 29.From the second expansion chamber 30, the fluid medium exits thedampener 20 via the dampener outlet 31 to a downstream piping system(not shown). The outlet 31 has an outlet cross-sectional area S_(O). Insome embodiments, such as the embodiment illustrated in FIGS. 5-7, theoutlet cross-sectional area S_(O) is approximately equal to thecross-sectional area S₄ of the second expansion chamber 30.

Referring to FIG. 7, the inside cross-sectional areas S₁, S₂, S₃, and S₄and the lengths L₁, L₂, L₃ and L₄ of the first contracting chamber 27,the first expansion chamber 28, the second contracting chamber 29, andthe second expansion chamber 30, respectively, are chosen to provide thedesired dampening of the fluid medium. Dampening can be measured interms of transmission loss. The transmission matrix is the acousticalpower difference between the incident and transmittal waves assuming ananechoic termination (i.e., without echo), which will be described ingreater detail below.

By determining the geometrical values that maximize transmission loss atthe desired ranges of frequencies, attenuation of those frequencies canbe achieved. However, in order not to diminish the mechanicaleffectiveness of a compressor, the pulsation dampener 20 should notincur too great of a pressure drop across the pulsation dampener 20 toachieve the desired transmission loss. Balancing the transmission losswith the pressure drop allows for attenuation of desired frequencieswithout diminishing fluid output from the pulsation dampener 20.

The transmission matrix mathematical expression is as follows:

$T = \begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix}$

This matrix is multiplied for each pipe junction. In the presentpulsation dampener 20, there are three junctions with three resultanttransmission matrices. The product of these three matrices yields asingle matrix denoted as T′.

$T^{\prime} = {{\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix}\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix}}\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix}}$

The equation used to describe each matrix follows:

$T = {^{{- j}\; {mk}_{c}l}\begin{bmatrix}{\cos \; k_{c}l} & {j\; Y_{o}\sin \; k_{c}l} \\{\frac{j}{Y}\sin \; k_{c}l} & {\cos \; k_{c}l}\end{bmatrix}}$

wherein j=√−1; m=mach number; k_(c)=ω/c(1−m²); ω=angular frequency;c=speed of sound; Y_(i)=c/S_(i); S_(i)=i^(th) pipe cross-sectional area;and I=length of pipe.

The transmission loss denoted TL is the acoustical power loss betweenthe incident and transmitted waves of an anechoically terminatedsilencer, or pulsation dampener. In terms of the transmission matrix T′,the transmission loss is calculated as follows:

${TL} = {20\; {\log_{10}\left\lbrack \frac{T_{11}^{\prime} + {\frac{S_{2}}{c} \cdot T_{12}^{\prime}} + {\frac{c}{S_{1}} \cdot T_{21}^{\prime}} + T_{22}^{\prime}}{2} \right\rbrack}}$

where S_(I) is the area at the inlet to the pulsation dampener 20 andS_(O) is the terminating area of the pulsation dampener (i.e., thecross-sectional area of the outlet 31, as described above).

The sudden increase in cross-sectional area (e.g., in an expansionchamber) and sudden reduction in cross-sectional area (e.g., in acontracting chamber) is the primary mechanism for the power loss. In asimpler form, the TL (transmission loss) for each junction within thepulsation dampener can be determined from:

TL=10 log₁₀(S _(i+1) +S _(i))²/(4S _(i+1) S _(i))

wherein S_(i+1) and S_(i) represent the pipe cross-sectional areachanges at each junction, as in FIG. 7. By way of example only, thecross-sectional areas of various portions of the fluid path 21 can berepresented by circles, and the cross-sectional areas can therefore becalculated from the respective diameters of such circles. For example,in a simple form, the first junction from contracting chamber 27 toexpansion chamber 28 can be described by the following incoming andoutgoing cross-sectional areas:

S ₁ =πD ₁ ²/4, and

S ₂ =πd ₁ ²/4.

Furthermore, the second junction from expansion chamber 28 tocontracting chamber 29 can be described by the following incoming andoutgoing cross-sectional areas:

S ₂ =πd ₁ ²/4, and

S ₃ =πD ₂ ²/4.

Finally, the third junction from contracting chamber 29 to expansionchamber 30 can be described by the following incoming and outgoingcross-sectional areas:

S ₃ =πD ₂ ²/4

S ₄ =πD ₂ ²/4

The frequency where the dampener 20 shows the greatest effectiveness isdetermined by the ¼ wavelength modes or L₁/4=c/f or L₁=4c/f. To tune theeffectiveness of the pulsation dampener 20 to specific frequencies, theneck length is chosen to be L₁=4c/f, wherein f is the frequency to beattenuated. The expansion area that follows would then be described as

TL=10 log₁₀(S _(i+1) +S _(i))/(4S _(i+1) S _(i)).

Thus, the neck lengths L₁, L₂, L₃ and L₄ determine the frequency atwhich the transmission loss is greatest, and the cross-sectional areasS_(i) and S_(i+1) determine the amplitude of that transmission loss. Amore exact calculation can be made using the transmission matrix. Giventhe complexity of the pulsation dampener 20, a numerical method ispreferably used to obtain the precise sizing.

FIGS. 8 and 9 illustrate another pulsation dampener 20′ according to thepresent invention, wherein like numerals represent like elements. Thepulsation dampener 20′ shares many of the same elements and featuresdescribed above with reference to the illustrated embodiment of FIGS.5-7. Accordingly, elements and features corresponding to elements andfeatures in the illustrated embodiment of FIGS. 8 and 9 are providedwith the same reference numerals followed by a prime sign (e.g., 20′,21′, 22′, etc.). Reference is made to the description accompanying FIGS.5-7 for a more complete description of the features and elements (andalternatives to such features and elements) of the embodimentillustrated in FIGS. 8 and 9.

As can be seen in FIGS. 8 and 9, the dampener 20′ can have variousconfigurations to facilitate connection in various piping systems. Forexample, as illustrated, the dampener 20′ may be a second stage dampenerwith a dampener body 22′ having a straight outlet end 26′ with astraight fitting 32′. Other configurations are also contemplated.

By configuring the pulsation dampener 20, 20′ appropriately, thedampener 20, 20′ mismatches acoustical impedances by contracting thenexpanding the fluid. The expansion volumes act as resonators, orresonating volumes, for attenuating high frequencies. By employing morethan one expansion volume in the fluid path 21, 21′, a desiredacoustical performance is achieved (e.g., a desired attenuation levelover a desired frequency range) without requiring that thecross-sectional area of the inlet 25, 25′ be significantly smaller thanpipes that feed the inlet 25, 25′ (e.g., an outlet from a compressor orpipes in fluid communication with an outlet of a compressor). Inaddition, because impinging the fluid medium on solid surfaces wouldincrease the pressure drop in the fluid medium, the pulsation dampener20, 20′ employs a smooth, contoured inner surface 17, 17′ of the body22, 22′ to inhibit impinging of the fluid medium on solid surfaces. Suchcontouring of the inner surface 17, 17′, in combination with the shapeof the fluid path 21, allows for the above-mentioned acousticalperformance while substantially reducing the pressure drop in the fluidmedium as it passes through the pulsation dampener 20, 20′.

In some embodiments, the pulsation dampeners 20 and 20′ of the presentinvention attenuate frequencies in the range of less than about 5000 Hz.In other words, the transmission loss achieved by the pulsationdampeners 20 and 20′ is sufficiently large in this frequency range. Insome embodiments, the pulsation dampeners 20 and 20′ attenuatefrequencies in the range of about 500 Hz to about 5000 Hz. In someembodiments, the pulsation dampeners 20 and 20′ attenuate frequencies inthe range of about 800 Hz to about 5000 Hz. In some embodiments, thepulsation dampeners 20 and 20′ of the present invention provide at leastabout 20 dB of attenuation in pressure pulsations in having a frequencyranging from about 500 Hz to about 5000 Hz. In some embodiments, thepulsation dampeners 20 and 20′ provide between about 20 dB and 40 dB ofattenuation in pressure pulsations having a frequency ranging from about500 Hz to about 5000 Hz. Of course, it should be understood that thegeometry of the pulsation dampeners 20 and 20′ of the present inventioncan be precisely controlled to achieve the desired transmission loss andattenuation across a desired range of frequencies, as described above.

Typically, performance of a silencer, or a pulsation dampener, is basedat least partially on two indicators: noise reduction index (NR) andtransmission loss index (TL). NR can be described as the differencebetween the sound pressure levels measured at the inlet (e.g., the inlet25 of the pulsation dampener 20) and the outlet (e.g., the outlet 31 ofthe pulsation dampener 20) of a dampener. That is,

${NR} = {{l_{P\; 1} - l_{P\; 2}} = {20\log_{10}\frac{P\; 1}{P\; 2}}}$

wherein l_(P1) is the sound pressure level at the inlet of a dampener,and l_(P2) is the sound pressure level at the outlet of a dampener. Whena sound pressure wave impinges on the inlet of a dampener, some of thesound pressure energy is transmitted through the dampener, while some ofit is reflected back. NR does not account for the reflected portion ofthe sound pressure energy. As mentioned above, TL is the change in theacoustical sound power between the incident and the transmitted waves ofan anechoicially terminated dampener. TL accounts for the differencebetween the sound power transmitted to the dampener and the sound powerthat exits the dampener. FIGS. 10 and 11 show a comparison of the P1/P2(i.e., the ratio of the sound pressure at the inlet to the soundpressure at the outlet, which is related to NR) and TL prediction forprior art venturis 10 and 15. Because TL is a widely accepted indicatorof a dampener's performance, TL is used to compare the performance ofthe prior art venturis 10 and 15 with the pulsation dampeners 20 and 20′of the present invention, as illustrated in FIGS. 10-13 and describedbelow.

FIG. 10 illustrates a transmission loss curve 50 and a pressure dropcurve 60 through the prior art venturi 10 illustrated in FIGS. 1 and 2for frequencies ranging from 0 to 5000 Hz. As shown in FIG. 10, thetransmission loss 50 through the ventur±10 varies greatly depending onfrequency, and exhibits many “dips” of greatly reduced transmission lossat various frequencies. For example, a first “dip” in transmission lossthrough the ventur±10 occurs at about 900 Hz. As a result, the venturi10 would be a poor pulsation dampener for airflow having a frequency ofabout 900 Hz. Furthermore, because of the many “dips” in thetransmission loss curve 50 throughout the frequency range illustrated(i.e., 0 to 5000 Hz), the venturi 10 is not an effective or useful meansto dampen pulsations across this frequency range. The ventur±10 mayeffectively attenuate pulsations for very narrow frequency ranges (e.g,from about 975 Hz to about 1000 Hz), but would not function robustly asa pulsation dampener according to the present invention.

FIG. 11 illustrates a transmission loss curve 70 and a pressure dropcurve 80 through the prior art venturi 15 illustrated in FIGS. 3 and 4for frequencies ranging from 0 to 5000 Hz. Similar to the transmissioncurve 50 describe above with respect to FIG. 10, the transmission loss70 through the ventur±15 varies greatly depending on frequency, andexhibits many “holes” and “dips” of zero or greatly reduced transmissionloss, respectively, at various frequencies. For example, a first “hole”in transmission loss occurs at about 1700 Hz for the venturi 15, and a“dip” occurs at about 2250 Hz. Similar to the venturi 10 illustrated inFIGS. 1 and 2, the venturi 15 illustrated in FIGS. 3 and 4 is not aneffective pulsation dampener at frequencies ranging from 0 to 5000 Hz.The ventur±15 may only effectively attenuate pulsations occurring atvery narrow ranges of frequencies (e.g., from about 975 to about 1000Hz).

FIG. 12 illustrates a transmission loss curve 90 for the pulsationdampener 20 illustrated in FIGS. 5-7 for frequencies ranging from 0 to5000 Hz. As shown in FIG. 12, the transmission loss 90 achieved by thepulsation dampener 20 occurs over a large range of frequencies. Forexample, the transmission loss curve experiences a “hole” around about2500 Hz, a first “dip” around about 3250 Hz, and a second “dip” aroundabout 4250 Hz. Other than these “holes” and “dips,” the transmissionloss is at least about 10 over frequencies ranging from about 500 toabout 2300 Hz, from about 2800 to about 3200 Hz, from about 3300 toabout 4200 Hz, and from about 4300 to about 4600 Hz. As a result, muchgreater ranges of frequencies are attenuated using the pulsationdampener 20 than the prior art venturis 10 and 15. The lengths (e.g.,L₁, L₂, L₃ and L₄) of the various sections of the pulsation dampener 20can be varied to position any “holes” or “dips” in transmission loss atfrequencies that are least important or relevant to a specificapplication using the relationship between neck length and frequencygiven above.

Furthermore, the pulsation dampener 20 also achieved a lower pressuredrop than that incurred with the prior art venturis 10 and 15. Fluidmedium is allowed to communicate between the outlet of a compressor (notshown) that is coupled to the inlet end 24 of the body 22, and in fluidcommunication with the inlet 25. As shown in FIGS. 5 and 6, fluid mediumis further allowed to flow through the fluid path 21 defined by the body22 of the pulsation dampener 20 to the outlet 31 without impinging onany solid surfaces, because the inner surface 17 is defined by roundedor contoured surfaces. For example, a first junction 92 is definedbetween the first contracting chamber 27 and the first expansion chamber28, a second junction 94 is defined between the first expansion chamber28 and the second contracting chamber 29, and a third junction 96 isdefined between the second contracting chamber 29 and the secondexpansion chamber 30. The inner surface 17 at, or adjacent, each of thejunctions 92, 94 and 96 is substantially smooth and contoured to inhibitimpinging the fluid medium on any solid surfaces as it flows through thefluid path 21, which reduces the pressure drop across each junction 92,94 of 96, and across the entire dampener 20.

FIG. 13 illustrates a transmission loss curve 100 for the pulsationdampener 20′ illustrated in FIGS. 8-9 for frequencies ranging from 0 to5000 Hz. As shown in FIG. 13, the transmission loss 100 achieved by thepulsation dampener 20′ occurs over a large range of frequencies. Forexample, the transmission loss curve experiences a “dip” around about1825 Hz. Other than this “dip,” the transmission loss is at least about10 dB over frequencies ranging from about 400 Hz to about 1820 Hz, andfrom about 1840 Hz to about 5000 Hz. As a result, much greater ranges offrequencies are attenuated using the pulsation dampener 20′ than theprior art venturis 10 and 15. The specific geometry of the pulsationdampener 20′ can be controlled using the equations and relationshipsdescribed above to position any “holes” or “dips” in transmission lossat frequencies that are least important or relevant to a specificapplication. Furthermore, the pulsation dampener 20′ also achieved alower pressure drop than that incurred with the prior art venturis 10and 15, due, at least in part, to the inner surface 17′ being roundedand contoured appropriately.

One factor that can make pulsation dampeners for air compressors acomplex problem to model is the presence of unsteady fluid flow thatbegins at compressor discharge port, to which the pulsation dampener isfluidly coupled.

One particularly effective location for a pulsation dampener, e.g., usedwith an oil-free screw compressor, is adjacent to the airend (or fluidend) discharge port, where the pressure pulsation is often greatest. Thepressure pulsation in the fluid can be described as slugs of fluid(e.g., air) that are discharged from the compressor each time rotors inthe compressor open and close. Such fluid flow, including thepulsations, is fluid dynamic by nature, and these pressure pulsationstravel at the convective speed of the fluid in the form of flowstructures that can be described as vortices.

Pressure pulsations in the fluid can be measured at the discharge portof the compressor. Typically, these pressure pulsations include a meanpressure component, and a fluctuating pressure component. For example,for a 100-psig compressor, the mean pressure component can be about 100psig, and the fluctuating pressure component can vary by ±30 psi. Theprimary frequency for the fluctuating pressure component isapproximately the frequency at which the discharge port of thecompressor opens and closes. In some embodiments, this frequency isgreater than about 500 Hz. Higher frequencies can also be present in thefluid stream, because the vortices (or similar flow structures) candivide into smaller vortices, and produce harmonic components. In someembodiments, the amplitude of the fluctuating pressure component of thepressure pulsation for the 100-psig compressor can be from about 70 psigto about 130 psig.

One purpose of the pulsation dampeners 20 and 20′ of the presentinvention is to convert the fluid dynamic pulsations described aboveinto acoustic pulsations by effectively squeezing the dischargevortices. The fluid pulsation that is discharged from the compressor,that enters the pulsation dampener 20 or 20′, can be decomposed into twocomponents: an acoustic component that has a wavelength, λ_(a), thattravels at the speed of sound, c, and a fluid dynamic component that hasa wavelength, λ_(g), that travels at the convective velocity of the gas,u_(g). In some compressor applications, the Mach number is less than0.2, which requires the acoustic wavelength to be greater than the fluiddynamic instability wavelength (i.e., λ_(a)>λ_(g)) for a givenfrequency. As the fluid progresses further into the pulsation dampener20 or 20′, the pressure pulsations transition from organized vorticalstructures to small-scale turbulent structures. As this transitionoccurs, the pulsations can become mostly acoustic rather than fluiddynamic. The pulsation dampeners 20 and 20′ of the present inventionaccomplish this transition both as a fluid dynamic device and as anacoustic device.

The pulsation dampeners 20 and 20′ of the present invention can provideseveral results. First, the pulsation dampeners 20 and 20′ can rapidlyconvert the fluid dynamic pressure pulsations discharged from the airendof a compressor to an acoustic pressure pulsation. Second, the pulsationdampeners 20 and 20′ can reduce the acoustic pressure pulsations byusing contraction and expansion chambers (such as those described aboveand illustrated in FIGS. 5-9). Third, the pulsation dampeners 20 and 20′can reduce the pressure pulsations in the fluid stream by using acontoured fluid path 21 or 21′ (as defined by the inner surface 17 or17′ of the pulsation dampener 20 or 20′) that minimizes the amount ofmean pressure loss (i.e., the fluid dynamic component of the pressurepulsations). The pulsation dampeners 20 and 20′ of the present inventioncan be designed to accomplish the desired attenuation of pulsationsusing acoustic and computational fluid dynamic computer software to makethe numerical predictions.

1. A method of attenuating fluid dynamic pulsations that propagatethrough a flow of fluid at a convective velocity of the fluid, thepulsations having an organized vortical structure, the methodcomprising: directing the flow to a pulsation dampener inlet having afirst area; transitioning the organized vortical structure to asmall-scale turbulent structure by squeezing the vorticies by passingthe flow of fluid through a passage having a second area that is smallerthan the first area, then rapidly expanding the flow of fluid by passingit into a chamber having a third area measured at an inlet of thechamber that is substantially larger than the second area; anddischarging the flow of fluid from the chamber, the flow of fluidincluding substantially attenuated fluid dynamic pulsations and acousticpulsations that travel through the flow of fluid at the speed of sound.2. The method of claim 1, further comprising attenuating the acousticpulsations by directing the flow of fluid from the chamber through aconverging diverging nozzle.
 3. The method of claim 1, wherein the flowof fluid enters the pulsation dampener inlet in a series of slugs havinga frequency that is proportional to a rotational speed of a compressor.4. A method of attenuating pulsations produced by the operation of acompressor, operation of the compressor producing fluid dynamicpulsations that propagate through a flow of fluid at a convectivevelocity of the fluid and acoustic pulsations that propagate through theflow of fluid at the speed of sound, the method comprising: convertingthe fluid dynamic pulsations to acoustic pulsations by firstconstricting the flow of fluid and then rapidly expanding the flow offluid; and attenuating the acoustic pulsations by passing the flow offluid through a converging diverging nozzle.
 5. The method of claim 4,wherein the converting step includes directing the flow of fluid througha converging nozzle.
 6. The method of claim 5, wherein the convertingstep includes directing the flow of fluid from the converging nozzle toan expansion chamber.
 7. The method of claim 6, wherein the convergingnozzle includes a minimum cross sectional area at an outlet and theexpansion chamber includes a maximum cross sectional area at an inlet,the inlet immediately adjacent the outlet.
 8. The method of claim 4,wherein the attenuating step includes directing the flow of fluidthrough a converging nozzle.
 9. The method of claim 8, wherein theattenuating step includes directing the flow of fluid through adiverging nozzle following passage through the converging nozzle. 10.The method of claim 9, wherein the converging nozzle and the divergingnozzle are positioned adjacent one another such that the rate of changeof the cross sectional areas along the flow path is continuous.
 11. Themethod of claim 4, wherein the rapidly expanding step includes passingthe flow of fluid through a junction having a first diameter on a firstside of the junction and a second diameter on the second side of thejunction, the second diameter being substantially larger than the firstdiameter.
 12. The method of claim 11, wherein the second diameter is atleast about four times the first diameter.
 13. A method of attenuatingpulsations in a flow of fluid produced by the operation of a compressor,the method comprising: directing the flow of fluid to a pulsationdampener inlet having a maximum diameter that defines a first crosssectional area; constricting the flow of fluid by passing it through aconstricting flow path having a minimum diameter that defines a secondcross sectional area that is smaller than the first cross sectionalarea; suddenly expanding the flow of fluid by discharging the flow offluid into a chamber having an inlet cross sectional area that issubstantially larger than the second cross sectional area, the inletcross sectional area being measured immediately adjacent the minimumdiameter of the constricting flow path; gradually constricting the flowof fluid by passing it through a chamber flow path in which the crosssectional area gradually reduces to a minimum third cross sectionalarea; gradually expanding the flow of fluid by passing it through anexpanding flow path in which the cross sectional area graduallyincreases to a maximum fourth cross sectional area; and discharging theflow of fluid from the pulsation dampener via an opening having anoutlet cross sectional area that is about equal to the fourth crosssectional area.